Method for forming a gas-permeable and ion-permeable membrane

Abstract

A method for forming a gas-permeable and ion-permeable membrane comprising fully impregnating a porous ion-impermeable or non-conductive polymer substrate with an ion-conducting polymer material to form a composite and subsequently stretching the composite to re-form pores in the substrate. The resulting membrane comprises regions of the ion-conducting material juxtaposed to the gas-permeable pores formed in the substrate by the stretching process.

What is claimed is: 
     
       1. A method for forming a membrane comprising gas-permeable regions and ion permeable regions, said method comprising the steps of: (a) providing a substrate comprising a porous ion-impermeable polymer;   (b) fully impregnating said substrate with a chosen polymeric ion-conducting material to provide a composite of regions of said ion-conducting material throughout said substrate;   (c) stretching said composite to produce pores in said substrate to provide for the passage of gas and to thereby form said membrane comprising regions of said ion-conducting material juxtaposed to said gas-permeable regions formed by said pores in said substrate.   
     
     
       2. The method of claim 1 wherein said substrate is selected from the group consisting of porous polytetrafluoroethylene, porous polypropylene, and porous polysulfone. 
     
     
       3. The method of claim 1 wherein said polymeric ion-conducting material is selected from the group consisting of a cation exchange material, an anion exchange material, and a cation and anion exchange material. 
     
     
       4. The method of claim 3 wherein said polymeric ion-conducting material is selected from the group consisting of a polymer of polytetrafluoroethylene with fluorinated ether side chains terminated with sulfonic acid groups, an alkali resistant copolymer of vinyl chloride and acrylonitrile with quaternary nitrogen groups, and polyethylene with acrylic acid radiation grafted thereon. 
     
     
       5. The method of claim 1 wherein said stretching is performed until said composite becomes opaque and white. 
     
     
       6. The method of claim 1 wherein said stretching is performed until the length of said composite is increased by about 10 to 20 percent. 
     
     
       7. The method of claim 1 wherein said substrate has a thickness within the range of about 0.025 to 0.25 millimeters (1 to 10 mils). 
     
     
       8. The method of claim 1 wherein: (a) said substrate comprises porous polytetrafluoroethylene;   (b) said polymeric ion-conducting material comprises a polymer of polytetrafluoroethylene with fluorinated ether side chains terminated with sulfonic acid groups; and   (c) said stretching is performed until said composite becomes opaque.   
     
     
       9. The method of claim 1 wherein said impregnating comprises: (a) providing a solution of said polymeric ion-conducting material in a chosen solvent;   (b) placing said solution on the surface of said substrate; and   (c) drying said substrate containing said solution to remove said solvent and thereby form said composite.   
     
     
       10. The method of claim 9 wherein said substrate containing said solution is dried partially, to form a partially wet composite, and further comprising: (a) dipping said partially wet composite into catalyst particles; and   (b) completing said drying of said composite, whereby said catalyst particles adhere to said composite.   
     
     
       11. The method of claim 1 further comprising prior to step "c", adhering catalyst particles to said composite.